1. Field of the Invention
The present invention relates in general to a numerical control system for a machine tool. More particularly, it relates to such a numerical control system capable of revising one of tool dimension compensation values when a spare tool which is designated in accordance with a numerical control program (hereafter referred to as "NC program" is attached to a tool spindle of the machine tool in place of the primary tool.
2. Description of the Prior Art
In a known numerical control system for a machine tool with an automatic tool changer, a spare tool which is prepared to replace a primary tool designated in accordance with an NC program is attached to a tool spindle of the machine tool in place of the primary tool when the same reaches the end of its life or is broken. At such time, a dimension compensation value registered for the primary tool can no longer be used for the spare tool. That is, it is usual that the dimension compensation value for the spare tool is different from that for the life-expired tool.
In order to obviate such inconvenience, in the known numerical control system, revision values which respectively correspond to spare tools being stored along with primary tools in the tool magazine are set in advance respectively in data setting devices, and when one of the spare tools is attached to the tool spindle, a corresponding one of the revision values is supplied to the numerical controller so as to revise a dimension compensation value designated in accordance with the NC program. Thus, the dimension compensation value being stored in the numerical controller for the primary tool is modified to represent the dimension compensation value for the spare tool.
However, in the known numerical control system, it is impossible to automatically modify the revision values being set in the date setting devices. Therefore, when the life of the spare tool also expires and when a secondary spare tool for the primary tool is attached to the tool spindle in place of the life-expired spare tool, manual data setting is required to change the revision value for adaptation to the secondary spare tool. Thus, the known numerical control system is caused to discontinue its automatic continuous operation when the life of the first spare tool expires.